Sign in to follow this  
George 47

PLiXiR Elite Melco Power Supply

Recommended Posts

Moderator
Posted (edited)

 

 

image.thumb.png.22c54422b1d2ac28bb5552eb8caae97a.png

 

In my previous review of the Melco digital library, I mentioned another box was sent by ADMM (UK distributor for both products), a PLiXiR power supply unit (PSU). This PSU was made specifically for the Melco with an output of 12V/2A although there is a 4A and 6A variant with more outputs. The PSU is contained inside a nicely made black aluminium and weighs 3 Kg so is reasonable chunky.

I have to admit I had a degree of scepticism about a PSU for a digital library. I have no problem with separate PSUs for amplifiers based on my practical experience with Border Patrol’s PSUs for valve amplifiers, Naim’s separate PSUs and noticing that whenever ARC improved their valve power amplifiers, they invariably improved the PSUs.

An amplifier is a straightforward device that accepts a 1-2V input signal, it then does some buffering and manipulation including splitting the voltage into two, the positive and the negative signal (Class B, A/B) and feeding the signal to the amplification stage, it is then recombined (with some feedback) and then out to the speakers. Straightforward. But in discussions with an amplifier designer, he thought of the amplifier in reverse. The aim is to get a small 1-2V signal and end up with a larger amplified output of some 10s of volts. However, those 10s of volts comes from the PSU. Therefore, a very clean and pure DC voltage is needed from the PSU as it will become the signal once it is modulated by the input signal. If the DC has any artefacts, they will appear in the output signal. So, the PSU is vital.

Many designers believe the only way to get an ultra-pure signal is to take the whole PSU out of the amplifier box and put it in a separate box where it can’t interfere with the audio signal. Naim does that with their 300 and 500 amplifiers, but they are not the only company.

The same applies to preamplifiers and I understand and get that.

But for a digital library? I was not so sure.

Looking at various designs of PSUs, the cheapest is the switch mode PSU (SMPSU). In this PSU the 230V is switched on/off at a very fast rate of between 50 kHz-1MHz. This PSU does away with big heavy transformers as only small ones are needed and they are therefore cheaper, smaller and more efficient. But they produce a lot of switching noise that has to be dealt with. Unfortunately, a lot of the plastic moulded SMPSU are bad at this. There are many videos on the web of people putting cables next to a switched-mode PSU and picking up a lot of the high-frequency switching noise. It is possible to significantly reduce this noise by careful design and filtration but of course, that costs. Linn has improved its switched-mode power supplies many times with gains in noise reduction as has Chord electronics.

But some designers think it is not worth the effort and stick with linear power supply units with big, heavy and costly transformers. There is now a significant industry of second supplier linear PSUs ranging in costs from a few £10s up to £4.5K, and probably beyond. These costs are not surprising as the PSU in an amplifier can be the major cost, bar the case.

It is claimed that the best, ultra-low noise type of linear PSU is one where a balanced transformer is used. These are specialised transformers that remove most of the noise and are made by just a few companies. In their most common use, they input 230V mains and output (by induction) 115V +, 115-   and an ultra-clean earth. For balanced transformers, the mains input can be very noisy, but as it does not directly connect to the output then all/most of the noise is removed and all that remains is the pure +115V, -115V and a 0V earth. In the PLiXiR a balanced mains transformer is used followed by the usual smoothing capacitors and voltage regulators to give a clean and well-regulated 12V. This outputs via a socket on the back of the box through a cable with a 2.1mm plug that fits into the back of the Melco digital library box.  

The use of a balanced transformer is recommended as the best way to treat mains by people such as Ben Duncan and Noel Keywood who have extensive experience in audio and are true measurists but with open minds on sound quality.

PLiXiR places a large label across their box stating in big letters, removal of this label voids the warranty. I, therefore, can only be vague about what happens inside the box. However, I did send them a list of questions to get some insight into what they have done. I believe the balanced transformer is from Noratel, who have an excellent reputation in transformers and supply them to many recording studios where clean mains is vital. 

image.thumb.png.031412412fa241cd883c58f8b9c17349.png

What are the key features of the PLiXiR PSU for the Melco?

 

The PLiXiR PSU is the Elite Balanced DC Power Supply.  It features 3 stages of noise isolation and filtration stage.  The first stage is a custom-wound transformer used in a special balanced configuration circuit (hence the balanced DC power supply).  We are the only manufacturer to use this method.  This ensures no diode noise injection into the circuit ground.  And as the circuit ground is referenced directly to transformer winding, there is minimal ground loop current as well between the circuit ground and the transformer winding.

The 2nd stage is the discrete component pre-regulator stage.  This gets rid of most of the noise in the DC supply line.  The equivalent capacitance is more than 1Farad for this circuit.

 The 3rd stage is the actual regulator stage.  As most of the noise is eliminated by the previous 2 stages, its performance is much improved and takes care of voltage regulation.  The product is short-circuit / over-current and overheat protected.  

What are the advantages of having a balanced 12V output?

 

As mentioned above, our definition of balanced is the use of the balanced circuit of the transformer.

Are filters used to reduce RFI/EMI?

 

No filters are used.  We don’t like RFI / EMI filters that rob dynamics from the music.  With a 3-stage design, no EMI / RFI will affect the equipment connected to the PLiXiR PSU.  This is unlike a normal, traditional simple 1 stage regulator design where you need to employ filters to reduce the insidious RFI and EMI.

What is the measured noise levels on the 12V output?

 

It is less than 0.1mV measured.

How do you minimise noise on the 0V reference voltage?

 

Our novel balanced transformer circuit ensures no diode noise injection into the 0V reference.   This already is a performance difference.  The use of a FULL 0V reference ground plane on the PCB ensures lowest impedance return path for ground currents and minimises noise on the 0V reference voltage as well. 

Is any switching used in the PSU?

 

There is no switching used in the PSU.  It is a fully linear design.

What type of capacitors/regulators are used?

 

We use low impedance high temperature industrial rated capacitors built for long life.  The 2nd pre-regulator stage is a discrete transistor design.  The final stage regulator is chosen for its low noise performance and safety features. 

Certainly, noise reduction is treated seriously and all of the components are encapsulated in a robust Aluminium box.

 

Sound Quality

 

So, what difference does it make (if any) to the sound quality of the Melco?

Well, I could cheat and say it improves the sound quality in the same way the Melco does to the original signal as described in my Melco review:

https://www.hifiwigwam.com/forum/topic/143340-melco-n100-digital-music-library/

But that is cheating. So, this is what I heard.

Dead Can Dance: Anastasis, Opium: The drums were far more natural and the different reverberation added to the drums was easier to hear. The music was better separated and it was as though each drum had been given its own acoustic space. The slight sharpness noticed with the Melco’s SMPS was gone leaving a very natural sound even though the music was created in a studio.

2 Cellos, Theme from Game of Thrones: Again, a larger soundstage with better separation. The cellos had a sharper, more natural sound that was more accurate as the Cellos were close-miked. It was easier to hear the tension build up in the track and finally dissipate but not completely as you await the program that follows.

Radiohead Weird Fishes/Apeggi: This track starts with some close-miked drums that set up a fast pace and the PLiXiR allowed a more natural sound through but it did not slow the pace, which other mains units do. The pace was fast. The moods of the song were more clearly heard as the tempo was easier to follow. It was also easier to translate the words of the song which may be a plus or minus depending on what you think about Thom Yorke’s writing.

Carles Piles Rossini William Tell Overture Finale: Yes, that one and no thoughts of HiHo Silver, please. The music starts with a very clear and distant sound that announces what is to come. This famous piece of music came through at a blistering pace and yes, ye olde foot was tapping and it was impossible not to want to get out of the chair and show the conductor how it should be done. It put a smile on my face and lifted the spirits.  The PLiXiR made it clearer and easier to hear.

And so, on it went. This PSU improved the music from the Melco by reducing the noise and making the background blacker. This gave the music a more 3D soundstage with the musical layers better separated. It did this without making it an audio autopsy (thanks to Martin for the phrase) and leaving the music a coherent whole.

The change the PLiXiR made is musically important and I missed it when I removed it from the circuit. Given the price of the Plixir Melco PSU (£500), I believe the PLiXiR is good value for money being about 25% the price of the Melco (£2,000) and it comes in a great looking and well-made box. So, I give this PSU a thumbs up and if you want to push the boundaries of the Melco then I suggest you try one out. You probably won’t send it back.  I didn’t.

Technical Specifications

 

OUTPUT

Less than 1mVrms residual noise at DC output. Output Current available 4 Amps current continuous. 

OUTPUT VOLTAGE

Output voltage available from 9 Vdc to 30 Vdc. Available in: 110 Vac or 230 Vac input voltage

CASING FINISH

Black anodized, sandblasted aluminium

WEIGHT

 3.2kg (4A) 

DIMENSIONS (IN MM)

230 x 160 x 70 

COMES WITH

Includes one-meter-long PLiXiR High Current DC Power Cable with a choice of 1.3mm, 1.7mm, 2.1mm or 2.5mm DC plugs to mate with your equipment.

Edited by George 47

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.
Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.